Integrated circuits, such as microprocessors and memory devices, include many metal-oxide-semiconductor field-effect transistors (MOSFETs), which provide the basic switching functions to implement logic gates, data storage, power switching, and the like.
Shielded gate trench MOSFETs are preferred for certain applications over conventional MOSFETs and conventional trench MOSFETs because they provide several advantageous characteristics. Shielded gate trench MOSFETs exhibit reduced gate-to-drain capacitance Cgd, reduced on-resistance RDSon, and increased breakdown voltage of the transistor. For conventional trench MOSFETs, the placement of trench gate to form vertical channel, while decreasing the on-resistance, also increases the overall gate-to-drain capacitance. The introduction of the shielded gate trench MOSFET structure remedies this issue by shielding the gate from the electric field in the drift region, thereby substantially reducing the gate-to-drain capacitance. The shielded gate trench MOSFET structure also provides the added benefit of higher minority carrier concentration in the drift region for the device's breakdown voltage and hence lower on-resistance. The improved performance characteristics of the shielded gate trench MOSFET make the technology an excellent choice for power switching applications such as the switching mode power supply (SMPS) commonly referred to as a synchronous buck converter (DC-DC converter).
The RDSon×QG, Figure of Merit (FOM) is generally considered one of the important indicators of MOSFET performance in SNIPS, where RDSON is the specific on-state resistance and QG is the gate charge. It generally requires a high blocking voltage (BV) and low on-state resistance (RDSon). In addition, the recent computing applications require the power MOSFET operate in high switching frequency. Thus, it is desirable to develop semiconductor power switching devices that can be switched at high speed and have high maximum blocking voltage capability and low on-state resistance.
It is within this context that embodiments of the present invention arise.